I have some cherries in my freezer (about 5lb) that I want to use to make a kriek. I've never brewed a lambic before and there are a lot of complicated techniques floating around, like turbid step mashes that are based on the Belgian traditions. My question is: can I do something simple like a single infusion mash? If the goal is to extract a large amount of dextrins, can't I just mash at a relatively high temperature, like 155F? Some argue that this will have sufficient tannins. I don't necessarily need a "traditional" brew, but rather a beer that is balanced and has an emphasis on the cherries.

As for the grist, does this work?
Pilsner 80%
White Wheat 10%
Munich 5%
Vienna 5%

For my first lambic, I did a simple wheat brew using a single infusion mash. The key with a lambic is to let it sit on the bugs for about a year, if not more. I put 10# of cherries (whole) in my lambic and let it sit on the bugs for almost 2 years. 3 months time really won't be enough to let the bugs do their work. My lhbs carries Wyeast and I used 3278 exclusively.

As for how much cherries to add, I like to be able to detect the fruit but not have it over-powering. To that end, I would say at least 2#, probably even 3#/gallon, if you use whole fruit.

Six months is definitely not long enough to ferment with that blend. I think you would be happiest if you let it sit for 12-24 months.

If you are really committed to only giving it six months, consider sour mashing your wort (either the whole thing over night or a portion for 24-72 hours) and then pitching a brett strain as the primary strain. You will get plenty of sourness and a little brett character. After one month, pitch the cherries and let them sit for another five months. You could go with a Belgian sacc strain and get a decent beer but I think the brett characteristics will make a much better beer.